BUPC Unbonded Prestressed Anchorage System
The BUPC unbonded prestressed anchorage system is the research result of Beijing Institute of Construction Engineering. The system passed the technical appraisal of the Ministry of Construction in 1981 and was one of the first batches of scientific and technological achievements promotion projects announced by the Ministry of Construction in 1991.
BUPC has built the first automatic extrusion complete set of unbonded prestressed tendons production lines in China, formed an anchor product processing system, and conducted an engineering test study on the long-term durability of unbonded prestressed for the first time in China.
2. Production of unbonded prestressed tendons
BUPC unbonded prestressed tendons are made by coating steel wire bundles or steel strands with lubricating anti-rust grease through special equipment and wrapping them with plastic sleeves.
The requirements for the protective layer of the unbonded prestressed tendons are: the grease of the coating layer should be sufficient and full, the thickness should be uniform, and no leakage is allowed; the thickness of the formed pipe wall should be uniform, the resistance to damage is strong, and the friction loss is small.
(1) Raw materials
Steel: Unbonded prestressed steel includes steel strands or 7-wire steel wire bundles with tensile strength from 1470MPa to 1860MPa.
Coating: The grease used for the unbonded prestressed tendons is a special construction grease, which has the characteristics of anti-rust, adhesion, acid resistance, good chemical stability, and a high melting point.
Wrapping material: low-density high-pressure polyethylene, with a low melting point, low viscosity, good fluidity, not easy to decompose in the processing temperature range, wide molding range, narrow crystallization temperature range, etc.
(2) Main process and flow
The characteristic of the prestressed tendon extrusion coating process is that after the oil-coated prestressed tendon is extruded, the plastic wrapper is formed on the prestressed tendon at one time. The main processes are eight processes including plate selection, hanging plate, steel wire forming, oiling, plastic coating, cooling, traction, and wire take-up.
3. Anchorage and coupler
BUPC’s anchorage system is specially designed for unbonded steel strands and is mainly divided into stressing anchors, dead-end anchors, and couplers. Stressing anchors are divided into two types: combined type and casting type.
(1) Stressing anchor
Combined stressing anchor: It is composed of an anchor head, wedge, and bearing plate, which work together.
Casting type stressing anchor: The anchor head and the bearing plate are integrated, and the casting type is adopted, which can reduce the size of the anchor and facilitate the arrangement of the component.
(2) Dead-end anchor
The unbonded steel strands can also use H-type bond head anchors.
The function of the unbonded strand coupler is mainly used to connect the length of the prestressed tendon.
4. Tensioning jack
The BUPC unbonded prestressing system is matched with the QYC270 mono strand jack. The characteristic of this jack is that the tool anchor is located at the front of the jack, which can be clamped and loosened automatically. The working length of the jack with the exposed prestressed tendons is only 20 or 25cm, and it is small in size, light in weight, and easy to operate.